1. Field of the Invention
The present invention principally relates to four-cycle engines for powering outboard motors. More particularly, the present invention relates to cooling and exhaust systems for such engines associated with outboard motors.
2. Description of the Related Art
Outboard motors are often used to power watercraft. The engines are attached to the back of the watercraft and serve to propel as well as push the watercraft. The engines include powerheads that often extend above a transom of the water. Because the engines are not substantially shielded from the front, the engines can be a large source of wind drag. Accordingly, efforts have been made to decrease the size of the outboard motors while not sacrificing engine performance. One way of decreasing the size of outboard motors employing v-type engines is to decrease the spread of the cylinder banks or to decrease the length of the cylinder banks.
A limitation on narrowing the cylinder banks involves the construction of most exhaust systems. The v-type engines currently used in outboard motors often include an exhaust system that routes the exhaust gases through the powerhead and into the drive shaft housing prior to expelling the gases to either the atmosphere or the body of water in which the watercraft is operating. These exhaust systems often include a pair of exhaust manifolds that separately funnel the exhaust gases from selected cylinders through an exhaust guide plate and into the balance of the exhaust system. The manifolds must be properly sized to allow sufficient exhaust gases to flow through the manifolds such that exhaust gas blow down removes sufficient exhaust gases from the combustion chamber. Accordingly, narrowing the valley between the cylinder banks on v-type engines could adversely affect performance due to the decrease in the exhaust manifold cross section.
Additionally, a seal must be maintained between the cylinder block and the exhaust guide plate to avoid gas leakage. Forming a proper seal, however, proves difficult if the sealed surface area becomes too large. Additionally, the cost of materials increases with the increases in the surface area to be sealed. The increase in materials cost is disadvantageous both upon initial sale as well as while completing repair work.
Accordingly, an improved exhaust and cooling system is desired whereby the engine size can be reduced without substantially sacrificing performance. In addition, the exhaust system should be designed for an efficient and cost effective manufacture of the outboard motors.
One aspect of the present invention involves an outboard motor comprising an internal combustion engine. An exhaust guide plate is positioned generally below the internal combustion engine and comprises an exhaust guide passage. The internal combustion engine comprises a generally vertically extending crankshaft and a cylinder block comprising a first cylinder bank and a second cylinder bank. The first cylinder bank and the second cylinder bank are inclined relative to each another with the first cylinder bank comprising a first lower cylinder and the second cylinder bank comprising a second lower cylinder. A first cylinder head assembly encloses the first lower cylinder and a second cylinder head encloses the second lower cylinder. The first cylinder head assembly comprises a first exhaust port and a first exhaust runner corresponding to the first lower cylinder and the second cylinder head assembly comprises a second exhaust port and a second exhaust runner corresponding to the second lower cylinder. The first exhaust runner extends between the first exhaust port and a first generally vertically extending exhaust manifold. The second exhaust runner extends between the second exhaust port and a second generally vertically extending exhaust manifold. A first connecting exhaust conduit communicates with the first exhaust manifold and a second connecting exhaust conduit communicates with the second exhaust manifold. The first connecting exhaust conduit extends toward the cylinder block and joins a first end of a first passage formed within the cylinder block. The second connecting exhaust conduit extends toward the cylinder block and joins a first end of a second passage formed within the cylinder block. The first end of the first passage is disposed vertically higher on the cylinder block than the first end of the second passage. The first and second passages merge within the cylinder block into an exhaust discharge and the exhaust discharge is coupled to the exhaust guide passage.
Another aspect of the present invention involves an outboard motor comprising an internal combustion engine. An exhaust guide plate is positioned generally below the internal combustion engine and comprises an exhaust guide passage. The internal combustion engine comprises a generally vertically extending crankshaft and a cylinder block having a pair of cylinder banks inclined relative to one another. Each of the pair of cylinder banks includes at least one cylinder and a corresponding exhaust port. An exhaust runner is in selective communication with each exhaust port. The engine comprises two exhaust manifolds that extend in generally vertical directions. The cylinder block also has a pair of passages formed therein that are in communication with the exhaust manifolds. The passages merge within the cylinder block into an exhaust discharge. The exhaust discharge is in communication with the exhaust guide passage. The engine further comprises a flywheel attached to the crankshaft and having an outer diameter. The exhaust discharge of the cylinder block is positioned within the cylinder block such that the outer diameter overlaps at least a portion of the exhaust discharge when viewed from the top.
A further aspect of the present invention involves an outboard motor comprising a first cylinder bank and a second cylinder bank, the first cylinder bank and the second cylinder bank being inclined relative to one another and jointly forming at least a portion of a cylinder block. A crankcase cover is connected to a portion of the cylinder block and at least partially defines a crankcase chamber. A generally vertically extending crankshaft extends through the crankcase chamber between the crankcase cover and the cylinder block. A first cylinder head assembly is attached to the first cylinder bank and a second cylinder head assembly is attached to the second cylinder bank. A first exhaust manifold is connected to the first cylinder head assembly and a second exhaust manifold is connected to the second cylinder head assembly. An exhaust passage is formed in the cylinder block and comprises a first branch, a second branch and a convergent portion that combines the first branch and the second branch. The first and second exhaust manifolds separately communicate with the first and second branches respectively. The first and second exhaust manifolds communicate with the first and second branches and the first and second exhaust manifolds are at least partially formed in the first and second cylinder head assemblies respectively.